The present invention relates to improved perpendicular magnetic recording media with improved signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d), for use with single-pole transducer heads. The present invention is of particular utility in the manufacture of data/information storage and retrieval media, e.g., hard disks, exhibiting ultra-high areal recording densities of about 200 Gb/in2 and greater with ultra-low noise characteristics.
Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density of the magnetic media. In this regard, so-called xe2x80x9cperpendicularxe2x80x9d recording media have been found to be superior to the more conventional xe2x80x9clongitudinalxe2x80x9d media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a xe2x80x9csingle-polexe2x80x9d magnetic transducer or xe2x80x9cheadxe2x80x9d with such perpendicular magnetic media.
It is well-known that efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (i.e., as compared to the magnetic recording layer), magnetically xe2x80x9csoftxe2x80x9d underlayer (xe2x80x9cSULxe2x80x9d), i.e., a magnetic layer having relatively low coercivity, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the xe2x80x9chardxe2x80x9d magnetic recording layer, e.g., of a cobalt-based alloy (e.g., a Coxe2x80x94Cr alloy) having perpendicular anisotropy or of a (CoX/Pd or Pt)n multi-layer superlattice structure. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the magnetically hard, perpendicular magnetic recording layer. In addition, the magnetically soft underlayer reduces susceptibility of the medium to thermally-activated magnetization reversal by reducing the demagnetizing fields which lower the energy barrier that maintains the current state of magnetization.
A typical perpendicular recording system 10 utilizing a vertically oriented magnetic medium 1 with a relatively thick soft magnetic underlayer, a relatively thin hard magnetic recording layer, and a single-pole head, is illustrated in FIG. 1, wherein reference numerals 2, 3, 4, and 5, respectively, indicate the substrate, soft magnetic underlayer, at least one non-magnetic interlayer, and vertically oriented, hard magnetic recording layer of perpendicular magnetic medium 1, and reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of single-pole magnetic transducer head 6. Relatively thin interlayer 4 (also referred to as an xe2x80x9cintermediatexe2x80x9d layer), comprised of one or more layers of non-magnetic materials, is provided in a thickness sufficient to prevent (i.e., de-couple) magnetic interaction between the soft underlayer 3 and the hard recording layer 5 but should be as thin as possible in order to minimize the spacing (HSS in the figure) between the lower edge of the transducer head 6 and the upper edge of the magnetically soft underlayer 3. In addition, interlayer 4 serves to promote desired microstructural and magnetic properties of the hard recording layer 5. As shown by the arrows in the figure indicating the path of the magnetic flux xcfx86, flux xcfx86 is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through vertically oriented, hard magnetic recording layer 5 in the region above single pole 7, entering and travelling along soft magnetic underlayer 3 for a distance, and then exiting therefrom and passing through vertically oriented, hard magnetic recording layer 5 in the region above auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 1, vertical lines 9 indicate grain boundaries of each polycrystalline (i.e., granular) layer of the layer stack constituting medium 1. As apparent from the figure, the width of the grains (as measured in a horizontal direction) of each of the polycrystalline layers constituting the layer stack of the medium is substantially the same, i.e., each overlying layer replicates the grain width of the underlying layer. Not shown in the figure, for illustrative simplicity, are a protective overcoat layer, such as of a diamond-like carbon (DLC) layer formed over hard magnetic layer 5, and a lubricant topcoat layer, such as a layer of a perfluoropolyethylene material, formed over the protective overcoat layer. Substrate 2 is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Alxe2x80x94Mg having an Nixe2x80x94P plating layer on the deposition surface thereof, or substrate 2 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; soft magnetic underlayer 3 is typically comprised of an about 2,000 to about 4,000 xc3x85 thick layer (or a pair of layers) of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, etc.; interlayer 4 typically comprises an up to about 10 xc3x85 thick layer (or layers) of at least one non-magnetic material, such as Pt, Pd, Ir, Re, Ru, Hf, alloys thereof, TiCr, and Co-based alloys; and hard magnetic layer 5 is typically comprised of an about 100 to about 250 xc3x85 thick layer of a Co-based alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B, iron oxides, such as Fe3O4 and xcex4-Fe2O3, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 xc3x85 thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, and Pt, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 10 xc3x85 thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and/or interfacial anisotropy (2nd type).
Another way of classifying perpendicular magnetic recording media into different types is based on the media properties provided by the material utilized for the magnetically hard recording layer. For example, as indicated above, the magnetically hard, perpendicular recording layer can comprise magnetic alloys which are typically employed in longitudinal media, e.g., CoCr alloys, or multilayer magnetic superlattice structures, such as the aforementioned (CoX/Pd or Pt)n superlattice structures. Representative M-H hysteresis loops of magnetic recording layers comprised of these different types of materials are shown in FIGS. 2(A)-2(B). As is evident from FIG. 2(A) showing the M-H loop of a perpendicular recording medium comprising a CoCr alloy, such type media typically exhibit a relatively low coercivity, low remanent squareness, i.e., less than 1, and a positive nucleation field Hn. In addition, the occurrence of magnetic domain reversal within bits, caused by the presence of high demagnetization fields in CoCr-based perpendicular recording media, is problematic with such media in that the phenomenon is a significant source of media noise reducing the SMNR. A high remanent squareness and a negative nucleation field Hn are required in order to obtain good bit stability.
By contrast, and as evidenced by FIG. 2(B) showing the M-H loop of a perpendicular recording medium comprising a (CoX/Pd)n multilayer magnetic superlattice structure, such type media advantageously exhibit a relatively high coercivity, remanent squareness of about 1, and a negative nucleation field Hn, which characteristics are attributed to the high anisotropy energy of such type media arising from interfacial anisotropy effects. However, the grains of the multilayer magnetic superlattice structure tend to experience exchange coupling leading to transition noise. Moreover, notwithstanding the possibility of further improvements in multilayer magnetic superlattice structures for use in the fabrication of high recording density magnetic media, significant current issues/problems remain pertaining to the ability to manufacture such structures in a commercially viable manner.
It is believed that high areal recording densities of about 200 Gbit/in2 or greater are possible with perpendicular magnetic media utilizing CoCr-based magnetic alloys as the magnetically hard recording layer. However, the obtainment of such high areal recording densities requires CoCr-based perpendicular media which exhibit the advantageous properties associated with multilayer magnetic superlattice-based media, i.e., high coercivity, remanent squareness of about 1, and a negative nucleation field Hn.
In view of the above, there exists a clear need for improved, high areal recording density, perpendicular magnetic information/data recording, storage, and retrieval media including CoCr-based magnetically hard recording layers, but which exhibit substantially increased signal-to-media noise ratios (SMNR), high coercivity, remanent squareness of about 1, and a negative nucleation field Hn. In addition, there exists a need for an improved method for manufacturing high areal recording density, perpendicular magnetic recording media employing CoCr-based magnetically hard recording layers which exhibit substantially increased SMNR, high coercivity, remanent squareness of about 1, and a negative nucleation field Hn, which media can be readily and economically fabricated by means of conventional manufacturing techniques and instrumentalities.
The present invention addresses and solves problems attendant upon the use of CoCr-based magnetically hard recording layers in the manufacture of high bit density perpendicular magnetic media, e.g., noise generation which adversely affects the SMNR of the media, while maintaining all structural and mechanical aspects of high bit density recording technology. Moreover, the magnetic media of the present invention can be fabricated by means of conventional manufacturing techniques, e.g., sputtering.
An advantage of the present invention is an improved low noise, high areal recording density, perpendicular magnetic recording medium.
Another advantage of the present invention is an improved, low noise, high areal recording density, perpendicular magnetic recording medium having a negative nucleation field Hn, remanent squareness of about 1, and high coercivity of at least about 5,000 Oe.
Still another advantage of the present invention is a method of manufacturing an improved low noise, high areal recording density, perpendicular magnetic recording medium.
Yet another advantage of the present invention is a method of manufacturing an improved low noise, high areal recording density, perpendicular magnetic recording medium having a negative nucleation field Hn, remanent squareness of about 1, and high coercivity of at least about 5,000 Oe.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a low noise, high areal recording density, perpendicular magnetic recording medium, comprising:
(a) a non-magnetic substrate having a surface; and
(b) a layer stack formed over the substrate surface, the layer stack comprising, in overlying sequence from the substrate surface:
(i) a magnetically soft underlayer;
(ii) at least one non-magnetic interlayer; and
(iii) a CoCr-based, magnetically hard perpendicular recording layer;
wherein the compositions of the at least one non-magnetic interlayer and the CoCr-based, magnetically hard perpendicular recording layer are selected to provide the medium with a negative nucleation field Hn, remanent squareness of about 1, and high coercivity of at least about 5,000 Oe.
In accordance with embodiments of the present invention, the at least one non-magnetic interlayer (ii) is not more than about 10 nm thick and comprises a layer of Ru, a Ru/CoCr bi-layer structure, or a Ru/CoCrX bi-layer structure, wherein X is at least one element selected from the group consisting of Pt, Ta, Mo, Ti, W, Ag, and Pd.
According to particular embodiments of the present invention, the at least one non-magnetic interlayer (ii) comprises a Ru/CoCr bi-layer structure, wherein the Cr content of the CoCr portion of the Ru/CoCr bi-layer structure is from about 37 to about 43 at. %, or a Ru/CoCrX bi-layer structure, wherein the Co content of the CoCrX portion of the Ru/CoCrX bi-layer structure is from about 57 to about 63 at. %.
According to further embodiments of the present invention, the CoCr-based, magnetically hard perpendicular recording layer (iii) is from about 10 to about 30 nm thick and comprises a CoCrPt alloy, e.g., with a Pt content from about 14 to about 21 at. %, such as a CoCrPt alloy comprising about 20 at. % Cr and about 15 at. % Pt; the magnetically soft underlayer (i) is from about 150 to 400 nm thick and comprises a material selected from the group consisting of: Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoTaZr, CoFe, Fe, FeN, FeSiAl, FeSiAlN, FeTaC, FeAlN, FeTaN, CoFeZr, and FeCoB, e.g., FeCoB; and the non-magnetic substrate (a) comprises a material selected from the group consisting of Al, NiP-plated Al, Alxe2x80x94Mg alloys, other Al-based alloys, other non-magnetic metals, other non-magnetic alloys, glass, ceramics, polymers, glass-ceramics, and composites and/or laminates thereof.
According to still other embodiments of the present invention, the magnetic recording medium further comprises:
(c) a protective overcoat layer over the magnetically hard perpendicular recording layer (iii); and
(d) a lubricant topcoat over the protective overcoat layer.
According to embodiments of the present invention, the non-magnetic substrate (a) comprises a material selected from the group consisting of Al, NiP-plated Al, Alxe2x80x94Mg alloys, other Al-based alloys, other non-magnetic metals, other non-magnetic alloys, glass, ceramics, polymers, glass-ceramics, and composites and/or laminates thereof; and
the layer stack (b) comprises:
a magnetically soft underlayer (i) from about 150 to 400 nm thick and comprised of FeCoB;
a non-magnetic interlayer (ii) not greater than about 10 xc3x85 thick, comprised of a Ru layer, a Ru/CoCr bi-layer structure, or a Ru/CoCrX bi-layer structure, wherein X is at least one clement selected from the group consisting of Pt, Ta, Mo, Ti, W, Ag, and Pd; and
a magnetically hard, perpendicular magnetic recording layer (iii) about 25 nm thick and comprised of a CoCrPt alloy with about 20 at. % Cr and about 15 at. % Pt;
and the medium exhibits a high coercivity of about 5,000 Oe, a remanent squareness of about 0.98, and a negative nucleation field Hn of at least about xe2x88x921,250 Oe.
Another aspect of the present invention is a method of manufacturing a low noise, high areal recording density, perpendicular magnetic recording medium, comprising the steps of:
(a) providing a non-magnetic substrate having a surface; and
(b) forming a layer stack over the substrate surface, comprising steps for forming in overlying sequence from the substrate surface:
(i) a magnetically soft underlayer;
(ii) at least one non-magnetic interlayer; and
(iii) a CoCr-based, magnetically hard perpendicular recording layer;
wherein step (b) includes selecting the compositions of the at least one non-magnetic interlayer and the CoCr-based, magnetically hard perpendicular recording layer to provide the medium with a negative nucleation field Hn, remanent squareness of about 1, and high coercivity of at least about 5,000 Oe.
According to embodiments of the present invention, step (a) comprises providing a non-magnetic substrate comprised of a material selected from the group consisting of Al, NiP-plated Al, Alxe2x80x94Mg alloys, other Al-based alloys, other non-magnetic metals, other non-magnetic alloys, glass, ceramics, polymers, glass-ceramics, and composites and/or laminates thereof;
step (b)(i) comprises forming the magnetically soft underlayer as an about 150 to about 400 nm thick layer comprised of a material selected from the group consisting of: Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoTaZr, CoFe, Fe, FeN, FeSiAl, FeSiAlN, FeTaC, FeAlN, CoFeZr, and FeCoB;
step (b)(ii) comprises forming the at least one non-magnetic interlayer at a thickness not greater than about 10 nm and comprised of a layer of Ru, a Ru/CoCr bi-layer structure, or a Ru/CoCrX bi-layer structure, wherein X is at least one element selected from the group consisting of Pt, Ta, Mo, Ti, W, Ag, and Pd; and
step (b)(iii) comprises forming the CoCr-based, magnetically hard perpendicular recording layer as an about 10 to about 30 nm thick layer comprised of a CoCrPt alloy with a Pt content from about 14 to about 21 at. %.
In accordance with a particular embodiment of the present invention:
step (b)(i) comprises forming a magnetically soft underlayer comprised of FeCoB;
step (b)(ii) comprises forming a non-magnetic interlayer wherein the portion of Co in the Ru/CoCr bi-layer structure or Ru/CoCrX bi-layer structure is from about 57 to about 63 at. %.
step (b)(iii) comprises forming a magnetically hard, perpendicular magnetic recording layer (iii) about 25 nm thick and comprised of a CoCrPt alloy with about 20 at. % Cr and about 15 at. % Pt;
whereby the medium exhibits a high coercivity of about 5,000 Oe, a remanent squareness of about 0.98, and a negative nucleation field Hn of at least about xe2x88x921,250 Oe.
According to an embodiment of the present invention, each of steps (b)(i), (b)(ii), and (b)(iii) for respectively forming the magnetically soft underlayer, the non-magnetic interlayer, and the magnetically hard, perpendicular recording layer comprises DC magnetron sputtering; and the method further comprises heating the non-magnetic substrate between steps (b)(i) and (b)(ii) and between steps (b)(ii) and (b)(iii).
Further embodiments of the present invention comprise steps of:
(c) forming a protective overcoat layer over the magnetically hard perpendicular recording layer; and
(d) forming a lubricant topcoat over the protective overcoat layer.
Still another aspect of the present invention is a low noise, high areal recording density, perpendicular magnetic recording medium, comprising:
(a) a perpendicular magnetic recording layer comprised of a CoCr alloy; and
(b) means for providing the medium with a high negative nucleation field Hn, remanent squareness of about 1, and a high coercivity of at least about 5,000 Oe.
A still further aspect of the present invention is a disk drive comprising a magnetic recording medium including a layer structure according to the present invention.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not limitative.